1. Technical Field
The present invention relates to an ink jet method and an ink jet apparatus.
2. Related Art
In the related art, various kinds of methods are used as a recording method of forming an image based on an image data signal on a recording medium such as paper. Among them, since an image is formed directly on a recording medium by ejecting ink only to a required image portion by a cheap apparatus, the ink can be effectively used and the running cost is cheap. Further, since the ink jet method produces little noise, the ink jet method is excellent as a recording method.
Recently, according to an ink jet recording method using photocuring-type ink in which monomers are photopolymerized (cured) by being irradiated with light, an image having excellent water resistance and wear resistance can be formed on a recording surface of a recording medium, so the ink jet recording method is used for manufacturing color filters, performing printing (recording) on printed circuit boards, plastic cards, plastic sheets, large signboards, and plastic parts, printing barcodes and dates, and the like.
For example, Japanese Patent No. 4335955 discloses an energy ray curing-type ink composition containing a colorant, a polymerizable compound, a photoinitiator, and a surface adjusting agent, in which the polymerizable compound includes a monofunctional monomer having an acryl equivalent weight of 300 or less and one ethylene double bond in one molecule and multifunctional monomer having an acryl equivalent weight of 150 or less and two or more ethylene double bonds in one molecule, the photoinitiator contains the α-aminoalkylphenone-based compound and a thioxanthone-based compound, and the surface adjusting agent contains a silicon-based compound having a polydimethylsiloxane structure. Also, Japanese Patent No. 4335955 discloses a technique of obtaining a highly reactive ink composition with a low viscosity appropriate for an ink jet recording method by containing the polymerizable compound only including a monofunctional monomer having an acryl equivalent weight of 300 or lower, and a multifunctional monomer having an acryl equivalent weight of 150 or lower (Paragraphs 0006 and 0007 in Japanese Patent No. 4335955).
Here, when printing is performed by using the ink composition disclosed in Japanese Patent No. 4335955 with an ink jet printer, the temperature of a drum conveying a recording medium increases in accordance with prolonged continuous printing of the ink jet printer and the temperature of the recording medium increases. At this point, a problem of a generation of curing wrinkles of the recorded matter become worse. The cause has been examined to find out that as the viscosity of the ink when being attached to the surface of the recording medium and irradiated is lower, the generation of the curing wrinkles is greater. If the same composition of the ink is used, when the temperature of the ink when being irradiated with ultraviolet light is high and the viscosity of the ink is low, generation of curing wrinkles is greater. The increase of the temperature of the ink when being irradiated with ultraviolet light is mainly caused by the increase of the temperature of the recording medium. As the cause of the increase of the temperature of the recording medium, the heat generation of the light source, the heat generation of the head, the increase of the temperature of a drum due to curing heat when the ink on the recording medium is cured, and the like may be considered. The increase of the temperature of the recording medium is noticeable in a UV printer that performs continuous printing at high speed, such as a UV label recording device, especially, in a line printer.